Scan-assisted mobile telephone

ABSTRACT

The invention relates to a method for scanning, in particular documents with the aid of a camera (K). The inventive method consists in combining an image sequence or a sequence of partial images in order to obtain a final image, projecting a reference model (F) onto the camera vision field and in compensating representational differences of different images on the basis of geometrical information of the model (F).

The invention relates to a method for scanning, in particular documentsas well as to a mobile telephone according to the preamble of claim 2.

The use of a camera, typically with a low resolution, for scanningdocuments is known. This involves the camera and/or the mobile telephonebeing moved over the document at a short distance from it. A final imageis generated from the images and/or partial images recorded in this way.

The images are recorded for example using a high scanning frequency oftypically 15 or 30 Hertz. For this reason, adjacent images have anextremely high image overlap. A high resolution final image can becontinuously established by adjoining narrow film strips from therespective image centre and allowing for the camera displacement.

Small variations in the distance between the camera and the document anda slight tilting of the camera which occurs with a hand-held cameranevertheless result in extremely troublesome changes in size in thedocument content displayed. The size changes must be adjusted to eachother in a first processing step, so that the high resolution finalimage can be constructed without errors. The determination of theposition of the camera sensor with respect to the document, particularlyin terms of the distance and tilting, is a fundamental and importantcondition for fault compensation. The calculation of the relativeposition information from successive images is a known approach, whichis extremely complex and provides results which are mostly veryunstable. In general, tiltings of the camera in relation to the documentcan only be determined with great difficulty, on the basis of therecorded image information by means of image processing.

The object of the invention is to facilitate the scanning of documentsusing a scanning method and a mobile telephone.

This object is achieved according to the invention for a method by meansof the features specified in claim 1 and for a mobile telephone by meansof the features specified in claim 2.

The method and/or mobile telephone according to the invention allows forthe rapid and robust determination of the relative position of thecamera sensor in respect of the document.

In accordance with the invention, a reference model is projected ontothe visual field of the camera. The evaluation of the geometry of thepattern in the images enables the compensation of the representationaldifferences in the images.

A small reference model is permanently projected onto the same positionwithin the visual field of the camera and is evaluated in the recordedimage by means of an image processing algorithm. The position of thesensor in relation to the document is uniquely determined in athree-dimensional space from the geometric information of the referencemodel projected onto the document surface and the reference modelrepresented in the sensor. The use of a reference model permits theextraction of the necessary geometric information for compensating therepresentational differences in images to be very robust and rapid usingthe methods of digital image processing and to be effected independentlyof the content of the scanned document.

A suitable reference model is for example a small reticule, which ispermanently projected onto the same position within the visual field ofthe camera. The position of the sensor in relation to the document isdistinctly determined in a three dimensional space from the informationof the reticule parameter (distance) and the relative length of thereticule axis (tipping in x and y direction).

SUMMARY OF THE ADVANTAGES OF THE METHOD

-   -   Rapidity and robustness in the determination of the relative        position of the sensor to the document    -   Extremely precise determination of the distance and the tilting        of the sensor irrespective of the content of the scanned        document

The invention is described below in more detail with reference to anexemplary embodiment shown in the drawing.

The method for the position determination of a camera K in relation to adocument (not illustrated in more detail), as shown in FIG. 1, isrealized for example on a mobile telephone or a mobile radio devicewhich has the following features:

-   -   Camera K for example on the rear side of the mobile telephone MT        for recording images from the surroundings    -   Processor for processing image information and for determining        the relative sensor position    -   Light-emitting diode L on the rear side of the mobile telephone        MT for projecting a reticule F into the visual field of the        camera (K).

The mobile telephone MT moves across the document at a slight distancetherefrom in order to scan a document for example. The characteristicfeatures of the projection of a reference model F for determining therelative sensor position are roughly sketched on an exemplary design.

Case a) in comparison with case b)

In cases a) and b) the camera is parallel to the document surface. Thedistance of the camera to the document is larger in case a) than in caseb). The projected reticule F in the camera image is thus smaller in caseb) than in case a). The reticule size is directly linked to the sensordistance and can be calculated in each instance from the detail screenof the camera.

Case c)

The camera K and/or the camera sensor is tilted in respect of the masterdocument. The position of the sensor in a 3-dimensional space inrelation to the document can be distinctly determined from the absolutesize of the reticule in conjunction with the information about therelative length of the reticule axis.

1. Method for scanning, in particular documents, using a camera (K), animage sequence or a sequence of partial images being combined into afinal image, in which a reference model (F) is projected onto the visualfield of the camera, and in which representational differences ofdifferent images are compensated on the basis of the geometricalinformation of the model (F).
 2. Mobile telephone (MT) with a camera (K)and with an image processing device for generating a final image fromthe images or partial images obtained during a scanning process,characterized by a projection device (L), by means of which a referencemodel (F) can be projected onto the visual field of the camera, andmeans of compensating for representational differences of the differentimages on the basis of the geometrical information of the model (F).